﻿Gooch 
  and 
  Morley 
  — 
  Determination 
  of 
  Gold. 
  261 
  

  

  Aet. 
  XXIX. 
  — 
  The 
  lodometric 
  Determination 
  of 
  Gold 
  ^ 
  by 
  

   F. 
  A. 
  Gooch 
  and 
  Fkedekick 
  H. 
  Morley. 
  

  

  [Contributions 
  from 
  Kent 
  Chemical 
  Laboratory 
  of 
  Yale 
  University— 
  LXXXVIIL] 
  

  

  In 
  a 
  recent 
  attempt 
  to 
  measure 
  small 
  amounts 
  of 
  gold 
  in 
  

   solution 
  by 
  titrating 
  with 
  sodium 
  thiosulpliate 
  the 
  iodine 
  set 
  

   free 
  in 
  the 
  action 
  of 
  an 
  excess 
  of 
  potassium 
  iodide 
  upon 
  auric 
  

   chloride, 
  Peterson* 
  has 
  been 
  led 
  to 
  conclude 
  that, 
  on 
  the 
  aver- 
  

   age, 
  one-half 
  more 
  thiosulphate 
  is 
  used 
  up 
  in 
  changing 
  the 
  

   characteristic 
  starch 
  iodide 
  blue 
  to 
  the 
  faint 
  rose 
  color 
  which 
  

   precedes 
  entire 
  bleaching 
  than 
  is 
  called 
  for 
  upon 
  the 
  theory 
  

   that 
  the 
  thiosulphate 
  is 
  simply 
  converted 
  to 
  the 
  tetrathionate 
  

   in 
  the 
  usual 
  manner. 
  Peterson 
  explains 
  the 
  anomaly 
  upon 
  the 
  

   hypothesis 
  that, 
  besides 
  acting 
  upon 
  the 
  free 
  iodine, 
  the 
  thio- 
  

   sulphate 
  is 
  used 
  up 
  coincidently 
  by 
  interaction 
  with 
  the 
  aurous 
  

   salt, 
  formed 
  in 
  the 
  reduction, 
  with 
  formation 
  of 
  a 
  gold 
  sodium 
  

   thiosulphate 
  on 
  the 
  type 
  of 
  the 
  well-known 
  silver 
  sodium 
  thio- 
  

   sulphate. 
  The 
  reaction 
  of 
  this 
  hypothesis 
  is 
  in 
  the 
  nature 
  of 
  

   things 
  most 
  improbable, 
  since 
  there 
  is 
  no 
  reason 
  to 
  suppose 
  

   that 
  the 
  soluble 
  double 
  thiosulphate 
  could 
  resist 
  the 
  action 
  of 
  

   the 
  free 
  iodine 
  which 
  is 
  present 
  to 
  the 
  end 
  — 
  the 
  appearance 
  of 
  

   the 
  rose 
  color, 
  — 
  and 
  our 
  study 
  of 
  the 
  reaction 
  of 
  sodium 
  thio- 
  

   sulphate 
  upon 
  the 
  mixture 
  of 
  gold 
  chloride 
  and 
  potassium 
  

   iodide, 
  the 
  account 
  of 
  which 
  follows, 
  discloses 
  no 
  evidence 
  of 
  

   the 
  consumption 
  of 
  more 
  thiosulphate 
  than 
  is 
  demanded 
  by 
  

   the 
  usual 
  theory, 
  which 
  postulates 
  the 
  simple 
  formation 
  of 
  the 
  

   tetrathionate 
  by 
  the 
  interaction 
  of 
  the 
  thiosulphate 
  and 
  free 
  

   iodine. 
  

  

  It 
  appeared 
  in 
  the 
  course 
  of 
  our 
  preliminary 
  experimenta- 
  

   tion 
  that, 
  while 
  practically 
  similar 
  results 
  were 
  obtained 
  by 
  

   adding 
  the 
  thiosulphate 
  until 
  the 
  blue 
  of 
  the 
  starch 
  iodide 
  had 
  

   changed 
  to 
  rose, 
  the 
  indications 
  were 
  somewhat 
  more 
  con- 
  

   cordant 
  when 
  the 
  final 
  rose 
  color 
  w^as 
  developed 
  by 
  adding 
  

   iodine 
  to 
  the 
  solution 
  from 
  which 
  the 
  blue 
  had. 
  been 
  bleached 
  

   to 
  colorlessness 
  by 
  a 
  shght 
  excess 
  of 
  the 
  thiosulphate. 
  

  

  It 
  appeared, 
  also, 
  that 
  the 
  reduction 
  of 
  the 
  auric 
  salt, 
  with 
  

   the 
  consequent 
  liberation 
  of 
  iodine, 
  is 
  conditioned 
  by 
  the 
  vol- 
  

   ume 
  of 
  the 
  solution, 
  the 
  mass 
  of 
  the 
  iodine 
  present, 
  and 
  the 
  

   time 
  of 
  action. 
  

  

  The 
  following 
  statement, 
  in 
  which 
  each 
  result 
  is 
  the 
  average 
  

   of 
  several 
  titrations 
  in 
  close 
  agreement, 
  shows 
  the 
  effect 
  upon 
  

   the 
  immediate 
  evolution 
  of 
  iodine 
  brought 
  about 
  by 
  adding 
  

   varying 
  amounts 
  of 
  water 
  to 
  the 
  gold 
  solution 
  before 
  introduc- 
  

   ing 
  the 
  iodide, 
  and 
  the 
  effect 
  of 
  different 
  amounts 
  of 
  iodide 
  at 
  

   different 
  dilutions. 
  

  

  *Zeiischr 
  fiir 
  Anorg. 
  Chem., 
  xix, 
  63. 
  

  

  